The Study Of Substituted Benzenes Quantitative Structure-Activity Relationship Using The Semi-Empirical Method Of Quantum Chemical Calculation

The organic pollutants of Substituted benzene compounds are mostly widely presented in the environments of industrial and agricultural wastewater, then flow to aquatic organisms, and cause some negative impacts on the growth、the development and the reproduction of aquatic organisms, and thus threats to human life and health A systematic study on the toxicity of substituted benzene compounds is very significant. Quantitative Structure-Activity Relationship (QSAR) is a very important method in the toxicity studies. It is a kind of quantitative relationship about the molecular structure parameters (molecular descriptors) and its Biological Activity, which is established by a variety of statistical methods. The key of QSAR model is to obtain the molecular descriptors. The common method is started from the solution of the Schrodinger equation. Through the basic physical approximations, the Schrodinger equation can be turned into Hartree-Fock-Roothaan equation. Based on solving the equation whether empirical parameters, we found ab initio and semi-empirical (semi-empirical) method. But the ab initio calculations for computer’s memory size and CPU requirements are very high, and the workload is huge and difficult. The calculation method of Molecular descriptor is obtained by the semi-empirical method. According to different approximate, the Semi-empirical method is divided into different categories. At present, AM1(Austin model1) method and the PM3(Parameterized Model number3) method are widely used in the semi-empirical algorithm.We found the Experimental data of96h LC50(Lethal Concentration50) with fathead minnow and48h EC50(concentration for50%of maximal effect) with Algae. They contain eight substituted benzene compounds (nitrobenzene, alkyl benzenes, halogenated benzenes, benzoic acid, phenol, aniline base, phenyl ester base, and phenyl ketene, and so on). They were taken randomly selected into the training set and the prediction set.Through the EPI suite software, we get the molecular structure. Through the Project leader module of Scigress Explorer7.7software, structure parameters were calculated by the AM1and PM3method. They include:logKow, hydrophobic parameters, electrical molecular structure, electrical parameters, orbital parameters (EHOMO, ELUMO), energy parameters, Polari ability, dipole moment, the heat of formation (by PM3method) and so on. By stepwise multiple regression analysis in the SPSS statistical software, the two QSAR models toxicity of aquatic organisms and molecular descriptors is established. The results show that the models have a statistically significance. Through cross-validation and prediction set, the external examination results show that the model have a good stability and predictive ability. It is very important in the study to explore the toxicity of organic compounds.